Embodiments of the present invention relate generally to an apparatus and method corresponding to a transceiver chip that is part of an optical serial data communications system, and more particularly to reception, signal conditioning, and filtering of multi-rate serial data signals received by the transceiver chip.
High-speed digital communication networks over copper and optical fiber are used in many network communication and digital storage applications. SONET, Ethernet and Fibre Channel are widely used communication protocols used today and continue to evolve to respond to the increasing need for higher bandwidth in digital communication systems.
The Open Systems Interconnection (OSI) model (ISO standard) was developed to establish standardization for linking heterogeneous computer and communication systems. The OSI model includes seven distinct functional layers including Layer 7: an application layer; Layer 6: a presentation layer; Layer 5: a session layer; Layer 4: a transport layer; Layer 3: a network layer; Layer 2: a data link layer; and Layer 1: a physical layer. Each OSI layer is responsible for establishing what is to be done at that layer of the network but not how to implement it.
Layers 1 to 4 handle network control and data transmission and reception. Layers 5 to 7 handle application issues. Specific functions of each layer may vary to a certain extent, depending on the exact requirements of a given protocol to be implemented for the layer. For example, the Ethernet protocol provides collision detection and carrier sensing in the data link layer.
The physical layer, Layer 1, is responsible for handling all electrical, optical, and mechanical requirements for interfacing to the communication media. The physical layer provides encoding and decoding, synchronization, clock and data recovery, and transmission and reception of bit streams. Typically, high-speed electrical or optical transceivers are the hardware elements used to implement this layer.
The Synchronous Optical Network (SONET) is an interface standard for synchronous optical fiber transmission, applicable to the Physical Layer of the OSI Reference Model.
SONET comprises a set of signal rates for transmitting and receiving serial digital data signals over optical fiber. The base rate (OC-1) is 51.84 Mbps. Multiples of the base rate are also provided. For example:                OC-3 (155.52 Mbps)        OC-6 (311.04 Mbps)        OC-12 (622.08 Mbps)        OC-24 (1.244 Gbps)        OC-48 (2.488 Gbps)        
It is desirable to use the same hardware to transmit and receive variable data rates since it is easier to develop and maintain only one system which can handle multiple tasks. In addition, switching and routing functions may be performed dynamically which improves the flexibility of the network.
However, possible problematic situations may occur when driving lower data rate signals into wide-bandwidth components. For example, when OC-3, OC-6, OC-12, or 1 Gigabit Ethernet rate signals are driven into OC-48 optical components, the signals may not be properly filtered.
FIG. 1 is an exemplary illustration of signal ringing that may occur in an eye pattern of a lower rate serial data signal (e.g., a 311 Mbps OC-6 signal) when the lower rate serial data signal passes through a filter stage having a wider bandwidth corresponding to a higher data rate serial data signal (e.g., an OC-48 signal). The filter stage has almost no filtering effect on the OC-6 signal. Ringing, overshoot, and undershoot as a result of impedance mismatches and discontinuities on the signal transmission path imposed on the OC-6 signal pass through the OC-48 filter stage and may result in bit errors.
FIG. 2 is an exemplary illustration of eye pattern corruption that may occur in an eye pattern of a lower rate serial data signal (e.g., an OC-12 signal) when the lower rate serial data signal passes through a wider bandwidth filter stage (e.g., an OC-48 filter stage). The eye pattern is not clean and is beginning to close, which may generate mask violations.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.